Composition brake shoes of the type to which the present invention relates generally comprise a metal back such as steel and a molded composition friction material bonded thereto. Generally a backing strip is interposed between the molded friction element to compensate primarily for the difference of thermal expansion between the metal plate and molded friction composition.
In the absence of such a strip the molded composition material has a tendency to fracture and/or separate from the steel backing plate.
The backing strip generally comprises a binder and fiber reinforcing material disbursed therein. Typically the binder has been essentially a rubber/resin mixture with fillers and fibers, such as asbestos, glass fibers, yarns, synthetic or natural.
More recently it has been common practice to utilize a ground rubber tire which includes synthetic and/or natural strands which has been used as the reinforcing material. The ground rubber tire contains oils which tends to reduce the adhesive characteristics of the backing strip thereby reducing the adherence to the steel back plate.
For a more detailed decription of the cord reinforced backing strip reference is made to U.S. Pat. No. 3,751,330.